Within 2 weeks after the OGTT, patients keep a journal of everything they ate and drank over 3 days. Patients are fed a selected meal the following evening and receive saline fluids IV overnight. During the night, patients receive 2 doses of oral doubly labeled water. The next morning, patients receive [1,2-13C]acetate IV. A liquid mixed meal (Ensure Plus) is ingested hourly throughout the day. Patients also undergo hood indirect calorimetry over 30 minutes twice to measure resting energy expenditure. All urine is collected.